Dehydrogenation of propane in the presence of CO2 over GaN/SiO2 catalysts: Relationship between the type of SiO2 and the activity

As a class of key building blocks in the chemical industry, propylene is mainly obtained from the by-product of naphtha steam cracking and refinery fluid catalytic cracking. Dehydrogenation of propane in the presence of CO2 (CO2-ODHP), as an on-purpose process for producing propylene, is one of the most potential alternative routes. In the present work, a series of mesoporous materials with different pore structures, namely SBA-15, MCF, KIT-6, and microporous materials of Silicalite-1 were synthesized via the hydrothermal method. These supports were further impregnated with 5 wt% GaN and applied in the CO2-ODHP. The effects of the support, especially the pore structure, acidic and basic properties, Si–OH species, redox characteristic, etc. on catalytic performance of GaN/SiO2 were studied. The 5GaN/Silicalite-1 catalyst (5 means 5 wt%) with a microporous structure, was vigorously disturbed by the extra-granular and intra-granular diffusion limitations, resulting in a low propylene selectivity. However, the Si–OH species in the Silicalite-1 could react with GaN to create more active sites of the Si–O–GaN species, resulting in the improvement of the propane conversion. The 3D interconnected mesopores of the KIT-6 are favorable to eliminate the extra-granular diffusion limitation, and no intra-granular diffusion limitation exists during the reaction. The combination of active sites and mass transfer properties of the catalysts could reduce the apparent activation energy of the reaction, offering an excellent catalytic activity. The present work gains insight into how to reasonably design an efficient GaN-based catalyst in the CO2-ODHP reaction, especially with microporous/mesoporous structures.